Nanowire growth on dissimilar material

ABSTRACT

The present invention relates to growth of III-V semiconductor nanowires ( 2 ) on a Si substrate ( 3 ). Controlled vertical nanowire growth is achieved by a step, to be taken prior of the growing of the nanowire, of providing group III or group V atoms to a (111) surface of the Si substrate to provide a group III or group V 5 surface termination ( 4 ). A nanostructured device comprising a plurality of aligned III-V semiconductor nanowires ( 2 ) grown on, and protruding from, a (111) surface of a Si substrate ( 3 ) in an ordered pattern in compliance with a predetermined device layout is also presented.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to growth of semiconductor nanowires onsilicon. In particular the invention relates to growth of III-Vsemiconductors protruding perpendicular to the surface of a Sisubstrate.

BACKGROUND OF THE INVENTION

Over recent years the interest in semiconductor nanowires hasintensified. Nanowires are also referred to as nanowhiskers, nanorodsand nanocolumns etc. For the purpose of this application the termnanowire is to be interpreted as a structure being in essentially inone-dimensional form and that is of nanometer dimensions in its width ordiameter. Such structures are commonly also referred to as nanowhiskers,one-dimensional nano-elements, nanorods, nanocolumns, nanotubes, etc.Although these terms imply an elongated shape the nanowires may havee.g. a pyramidal shape. Usually nanowires are considered to have atleast two dimensions not greater than 100 nm. However, nanowires havinga diameter or width of about 1 μm can be formed. Controlling theone-dimensional growth on the nanometer scale offers uniqueopportunities for combining materials, manipulating properties, bothmechanical and electromagnetical, and to design novel devices. One ofthe useful devices that can be made due to the controlledone-dimensional growth of nanowires is light emitting diodes (LED).

Epitaxial growth of III-V semiconductors on Si presents severaldifficulties such as lattice mismatch, differences in crystal structure(III-Vs have a polar zincblende or wurtzite structure whereas Si has acovalent diamond structure), a large difference in thermal expansioncoefficient and the formation of so called anti-phase domains. Much workhas been done on planar growth of III-V materials on Si using differentapproaches attempting to grow device quality structures, see e.g. S. F.Fang et al., Gallium-Arsenide and Other Compound Semiconductors onSilicon, Journal of Applied Physics 68, R31-R58 (1990) for a review.

It is recognized that a III-V semiconductor nanowires grown out from anSi substrate would probably overcome several of the above mentionedproblems, due to the small cross-section of the conjunction between thenanowires and the Si substrate. In many systems nanowires grow in a<111> direction and most commonly in the [111]B direction. The growth ofnon-vertical wires from Si(111) substrates is commonly observed, seee.g. A. L. Roest et al., Position-controlled epitaxial III-V nanowireson silicon, Nanotechnology 17, (11), S271-S275 (2006), and poses aproblem in terms of process control. There are four <111> directionsavailable from the non-polar Si(111) substrate where only one isvertical as illustrated in FIG. 1 a. In industrial applications this mayhinder an efficient processing and lower the yield of useful components.

SUMMARY OF THE INVENTION

The prior art methods of producing nanowires or nanostructures of III-Vsemiconductors on Si substrates needs improvements in order to beuseable for large scale production of semiconductor devices.

The object of the present invention is to overcome the drawbacks of theprior art. This is achieved by the method and the device as defined inthe independent claims.

A method of producing a nanostructured device in accordance with theinvention comprises the steps of:

-   -   providing group III or group V atoms to a (111) surface of a Si        substrate in order to provide a group III or group V surface        termination; and    -   growing at least one III-V semiconductor nanowire from the (111)        surface of the Si substrate.

In one embodiment of the method in accordance with the invention themethod comprises the steps of:

-   -   providing a group III or group V material, such as Ga or In,        pre-flow at a predetermined elevated temperature to provide a        group III or group V material-terminated Si(111) surface giving        diffusion of the group III or group V material into a growth        catalyst particle/Si interface, and formation of a group III or        group V material layer in the growth catalyst particle/Si        interface;    -   a short growth step at a high temperature to form a thin        nucleation layer; and    -   lowering of the temperature to the temperature regime normally        used for nanowire growth and performing axial nanowire growth.

In one embodiment of the method in accordance with the invention aplurality of nanowires are grown on the (111) surface in an orderedpattern in compliance with a predetermined device layout.

A nanostructured device according to the invention comprises a pluralityof semiconductor nanowires, preferably made of III-V material, grown ona (111) surface of a Si substrate. Substantially all nanowires of thenanostructured device protrude perpendicular to the (111) surface.Preferably the nanowires are grown on the (111) surface of the Sisubstrate in an ordered pattern in compliance with a predetermineddevice layout. The ordered pattern may be a periodic pattern.

Thanks to the invention it is possible to provide III-V nanowires on Sisubstrates in only one predetermined direction. Such structuresfacilitate the growth of a single-domain coalescence layers with thenanowires as templates or the manufacturing of semiconductor devices forelectronic, optoelectronic, photonic, light emitting diode applications,etc.

Embodiments of the invention are defined in the dependent claims. Otherobjects, advantages and novel features of the invention will becomeapparent from the following detailed description of the invention whenconsidered in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the accompanying drawings, wherein:

FIG. 1 a schematically illustrates four available <111> directions froma FCC (111) surface, wherein, in the case of a polar III-V (111)Bsurface, the arrow 1 indicates a <111>B direction whereas the otherarrows denote <111>A directions;

FIG. 1 b is a top view of GaP nanowires grown on a (111) surface of a Sisubstrate according to a prior art method;

FIG. 2 schematically illustrates a) a Si (111) surface, b) a GaP (111)Bsurface (middle diagram), and c) how a monolayer of Ga-atoms on the topsites on the Si(111) renders the surface (111)B-like according to theinvention;

FIG. 3 schematically illustrates a) the initial stage where the catalystparticle is placed on the substrate and the surface termination iscompleted and b) a vertical nanowire on a Si-substrate grown on thesurface terminated Si (111) surface of the substrate according to theinvention;

FIG. 4 is a flow chart of a method of producing a nanowire according tothe present invention;

FIG. 5 schematically illustrates an example of a growth cycle resultingin nanowires protruding preferentially in an orthogonal direction from aSi (111) surface according to the invention;

FIG. 6 is a flow chart of one embodiment of a method comprising pre-flowof group III or group V material and a high temperature growth stepaccording to the invention;

FIG. 7 a is a scanning electron microscope (SEM) image of GaP/GaAsnanowires grown from a Si (111) surface according to the invention,wherein the yield was close to 100% over the entire sample; and

FIG. 7 b is a SEM image of nanowires where the growth was successfullycombined with lithographic methods (in this case electron beamlithography) to produce arrays of site-controlled nanowires protrudingnormal to the surface of the Si substrate;

FIG. 8 a schematically illustrates a coalescence layer grown from thenanowires according to the invention;

FIG. 8 b is a SEM image showing nanowire LEDs on GaP and based onvertical nanowires on a Si substrate according to the invention, whereinthe edge of the contact layer is visible so the both contacted anduncontacted LEDs can be seen, the device structure is schematicallyillustrated and in the right upper insert is an optical micrograph ELfrom a single electrically probed nanowire LED seen from the side;

FIG. 9 is SEM images of a) nanowires grown on GaP, b) nanowires grown onSi, c) ordered array of GaAs nanowires grown on Si, and d) schematicillustration of the structure of the first growth run, being the samenanowire structure used for photoluminescence (PL) measurements;

FIGS. 10 a-c are PL graphs of nanowires grown on a Si substrateaccording to the present invention; and

FIG. 11 shows a) power dependence of electroluminescence (EL) of GaAsLEDs grown on GaP and Si, b) EL spectra from GaP and Si based LEDnanostructures, c) the radiation pattern with the seed particle, and d)the radiation pattern with the seed particle removed.

DETAILED DESCRIPTION OF EMBODIMENTS

On many semiconductor substrates nanowires grow in a <111> direction andmost commonly in the [111)B direction. However, the growth ofnon-vertical wires from Si(111) substrates is commonly observed andposes a problem in terms of process control. As schematicallyillustrated in FIG. 1 a, there are four <111> directions available fromthe non-polar Si(111) substrate where only one, in the figure denoted 1,is vertical, i.e. at 90° angle to the substrate. The term vertical isinterpreted is for the purpose of this application interpreted as thenanowire is protruding from the substrate in a direction perpendicularto the substrate. The terms vertical and perpendicular, as well as theterms orthogonal and normal to, are used interchangeably throughout theapplication. A 100% yield of vertical nanowires protruding from thesubstrate is desired. Although highly aligned vertical III-V nanowiresgrown on Si have been demonstrated, see T. Mårtensson et al., EpitaxialIII-V nanowires on silicon, Nano Letters 4, (10), 1987-1990, 2004, largearea uniformity with respect to the growth direction and especiallyvertical growth from lithographically defined gold nanoparticles orgrowth catalyst particle need to be improved. A second challenge is toachieve well defined growth of nanowires on predetermined positions andin predetermined patterns on Si, and also to do this with nanowiresaligned in the [111] direction vertical to the (111) surface of a Sisubstrate. A typical example of GaP nanowires grown on Si(111) accordingto prior art methods is shown in FIG. 1 b, where the nanowires protruderandomly in the four <111> directions.

Although the Si surface is non-polar (lacks A and B-sides) it would beenough with one monolayer of either group III or group V atoms to turnit into a (111)B or (111)A-like surface, respectively. FIGS. 2 a and 2 bschematically illustrate the atomic arrangement of a Si(111) surface anda GaP(111)N surface, respectively. FIG. 2 c schematically illustratesthe atomic arrangement of a Si(111) surface with Ga atoms bound to theSi dangling bonds. Observe that a group III monolayer on Si provideswhat is normally termed a B-like (group V) termination for the III-Vsemiconductors, which may be somewhat counterintuitive.

A pre-flow of a metalorganic precursor, for example a group IIIprecursor such as TMGa for Ga or TMIn for In, before growth using metalorganic vapor epitaxy (MOVPE) could render the otherwise non-polar Sisurface “(111)B-like” by providing a Ga atom termination layer. Combinedwith the strong preference of nanowire growth along the [111]Bdirections, such a surface will favor vertical growth.

A further advantage is the small cross-section of the nanowires wheregrowth is generally believed to proceed layer by layer with one singlenucleation event per layer. So called anti-phase domains are thus notexpected to form since they require two or more nucleation events perlayer. Furthermore, when the nanowires are grown on a (111) facet of adiamond structure material as Si, the small footprint in combinationwith the unique directional properties of (111)B III-V nanowires willinhibit the formation of anti-phase-domain boundary defects, consideredto be a major technology barrier for realization of many semiconductordevices comprising Si substrates

Referring to FIG. 3 and FIG. 4, one embodiment of a method of producinga nanostructured device according to the invention comprises the stepsof:

-   -   100 providing group III or group V atoms to a (111) surface of a        Si substrate 3 in order to provide a group III or group V        surface termination 4; and    -   110 growing at least one III-V semiconductor nanowire 2 from        the (111) surface of the Si substrate 3.

FIG. 3 schematically illustrates two stages in the production of thenanostructured device. FIG. 3 a shows the situation with a growthcatalyst particle 10 with the surface termination 4 prior to nanowiregrowth, and FIG. 3 b illustrates a Si substrate 3 having a (111) surfaceand a vertical nanowire 2 that preferably is epitaxially grown in the(111) direction from the (111) surface. The final nanostructured devicemay include the growth catalyst particle 10, e.g. an Au-particle, oralternatively the growth catalyst particle 10 can be removed. Moreovergrowth methods not requiring a metallic growth catalyst particle 10 canbe used.

One important feature of the structure formed according to the method ofthe invention is as mentioned that the angle α between the Si(111)surface and the nanowire is about 90° as illustrated in FIG. 3 b. Thanksto the invention the certainty of growing at least one nanowire in adirection perpendicular to the Si substrate is improved. Furthermore themethod provides a high yield with respect to the growth direction whengrowing a large number of nanowires, i.e. substantially all nanowiresprotrude perpendicular to the (111) surface of the Si substrate.

As appreciated by a person skilled in the art, the angle α may slightlydeviate from the 90°, due to e.g. disordering, defects, strain etc. inthe initial nanowire growth. In one embodiment preferably at least 95%,more preferably 100% of said substantially all nanowires 3 have an angleα to the (111) surface of the Si substrate of 90°±5°. In anotherembodiment at least 90%, preferably at least 95%, more preferably 100%of said substantially all nanowires (505) have an angle (550) to the(111) surface of the Si substrate of 90°±2.5°. In addition the Sisubstrate may be cut in such way that that the surface does not followthe (111)-plane of the Si material. Thereby nanowires protruding fromthe surface of the Si substrate may have a different angle to thesurface.

Referring to FIG. 5 and FIG. 6, one embodiment of the method inaccordance with the present invention comprises:

-   -   100 providing group III or group V atoms to a (111) surface of a        Si substrate 3 in order to provide a group III or group V        surface termination 4 by 120 providing a group III or group V        material pre-flow at a predetermined elevated temperature to        provide a group III or group V material-terminated Si(111)        surface giving diffusion of the group III or group V material        into a growth catalyst particle/Si interface, and formation of a        group III or group V material layer in the growth catalyst        particle/Si interface;    -   130 a short growth step at a high temperature to form a thin        nucleation layer;    -   140 lowering of the temperature to the temperature regime        normally used for nanowire growth and performing axial nanowire        growth; and    -   110 growing at least one III-V semiconductor nanowire 2 from        the (111) surface of the Si substrate 3.

FIG. 5 schematically illustrates one implementation of the growth cycleoutlined above that was successfully used to produce nanowires whereclose to 100% grew in the vertical [111] direction as shown in FIG. 7.The temperature was ramped up to 625° C. under a 100 mbar hydrogenatmosphere. After 10 min of annealing, a 5 s TMGa pre-flow was appliedto render the surface Si(111):B-like and create a gold-gallium alloy.Subsequently both TMGa and PH₃ were introduced for 10 s to grow a thinGaP nucleation layer with (111)B orientation. Subsequently thetemperature was lowered to 475° C. under a PH₃ flow. By using the samegrowth conditions as on III-V (111)B substrates, nanowire growth of e.g.GaP or GaAs could be achieved with high quality as shown in FIG. 7 a.Using this nucleation method also lithographic patterning could be usedwith good results as shown in FIG. 7 b. Control of position anddirection of III-V nanowires on Si substrates are crucial parametersneeded for successful fabrication of optical devices on Si, as well asmost other nanowire applications where Si substrates are advantageous.

A short growth step at a higher temperature was also used by Tateno etal., Vertical GaP nanowires arranged at atomic steps on Si(111)substrates, Applied Physics Letters 89, (3), 033114 (2006), but itsfunction was not further discussed and the group III pre-flow was notused.

The above considerations may be summarized by the following procedurefor nucleation and subsequent nanowire growth.

-   -   (i) Providing a Ga pre-flow at elevated temperature to provide a        Ga-terminated Si(111) surface.        -   a. The exact temperature and time will vary for different            column-III material, as two different mechanisms needs to be            satisfied:            -   i. Diffusion of Ga (III-element) into the growth                catalyst particle/Si interface            -   ii. Formation of a Ga layer in the growth catalyst                particle/Si interface    -   (ii) A short growth step at a high temperature to form a thin        GaP (111)B nucleation layer    -   (iii) Lowering of the temperature to the temperature regime        normally used for nanowire growth and performing axial nanowire        growth.

The procedure is also applicable for other group III and group Vmaterials, and in the case of In it would comprise the following steps.

-   -   (i) Providing a In pre-flow at elevated temperature to provide a        In-terminated Si(111) surface.        -   a. The exact temperature and time will vary for different            column-III material, as two different mechanisms needs to be            satisfied:            -   i. Diffusion of In (III-element) into the growth                catalyst particle/Si interface            -   ii. Formation of a In layer in the growth catalyst                particle/Si interface    -   (ii) A short growth step at a high temperature to form a thin        GaP (111)B nucleation layer    -   (iii) Lowering of the temperature to the temperature regime        normally used for nanowire growth and performing axial nanowire        growth.

Since the Ga or In is only needed at locations where the nanowires areto be grown, it may be desirable that it is only injected into the gold.This can be achieved by bringing in the metalorganic molecules at atemperature that is below the cracking temperature of the molecule, buthigh enough so that it can be efficiently cracked with the gold as acatalyst. Gas flows can be controlled with a very high precision inMOCVD reactors, making this process very reproducible and homogenous.The illustration in FIG. 3 a shows one embodiment where the terminationcovers the entire substrate surface, however, the invention is notlimited to this.

In an example of the surface termination process comprising Indium, thesubstrate is heated to 350° C., and exposed to a flow of TMIn for 2minutes. Thereafter, the substrate is heated to 650° C. and kept at saidelevated temperature for 10 minutes to achieve the In-termination of theSi(111) surface by diffusion of In within the growth catalyst particle.Subsequently, a GaAs nucleation layer is grown by introducing a flow ofTMGa for 5 seconds followed by a flow of both TMGa and AsH₃ for 10seconds. Then the substrate temperature is lowered to 475° C. keepingthe flow of AsH₃. When the lower temperature of 475° C. is achieved, thegrowth of the vertical nanowire is initiated by introducing TMGa inaddition to the AsH₃ for 4 to 8 minutes. The structure is then slowlycooled down to room temperature in a continuous flow of AsH₃.

As is apparent for the person skilled in the art, and as discussedabove, Ga or In, and the formation of a Ga or In termination in thegrowth catalyst particle/Si interface is a non-limiting example asregards to materials.

With this method it is also possible to realize well defined growth ofnanowires on any etched, or in other fashion fabricated (111) surface,for example etched ridges on (001) Si Substrates.

The method is transferable to III-V nanowire growth on other diamondstructure substrates as Ge and C etc.

The method according to the invention can be combined with variouspatterning techniques, and offers a unique approach for providingprecisely positioned vertical III-V nanowires on a Si(111) surface.

A nanostructured device according to the present invention comprises aplurality of semiconductor nanowires 2, preferably made of a III-Vmaterial, grown on a (111) surface of a Si substrate 3, whereinsubstantially all nanowires 3 protrude perpendicular to the (111)surface. Preferably said substantially all nanowires 2 are grown in a(111)B direction.

As indicated above the ability to precisely position individualnanowires or a plurality of nanowires is essential in many applicationsin order e.g. to be able to manufacture semiconductor devices forelectronic, optoelectronic, photonic, light emitting diode applications,etc. In addition, preferably all nanowires should be directed in thesame direction from the substrate surface. In one embodiment of thenanostructured device according to the present invention the nanowiresare grown on the (111) surface in an ordered pattern in compliance witha predetermined device layout.

Each nanowire 2 may positioned at a predetermined position on the (111)surface of the Si substrate 3 with a positional deviation from thepredetermined position is no more than half the diameter of thenanowire, preferably no more than 20% of the diameter of the nanowire,more preferably no more than 5% of the diameter of the nanowire, stillmore preferably no more than 1% of the diameter.

FIG. 7 shows that substantially all nanowires can be grown in adirection perpendicular to the (111) surface. In a nanostructured deviceaccording to one embodiment of the present invention at least 90%,preferably at least 95%, more preferably 99%, still more preferably 100%of the nanowires protrude perpendicular to the (111) surface. Asmentioned above the angle α of the nanowires to the surface of thesubstrate may deviate slightly from 90°.

In one embodiment of a nanostructured device according to the presentinvention the nanowires are grown on the (111) surface in a periodicpattern.

In another embodiment of a method according to the present invention thenanostructured device comprises a coalescence layer 20 grown from thenanowires 2. Referring to FIG. 8 a, a plurality of vertically alignednanowires 2 protruding from a substrate can be used as templates forre-growth of continuous III-V semiconductor layers. Continuous III-Vsemiconductor layers grown on Si usually exhibit a high amount of antiphase domains. In the present invention the preferential (111)Bdirectional growth of individual nanowires and the initial nucleation ofonly one sub material on only one of the two Si fcc sub lattices for allnanowires will ensure that all these nanowires share the same crystaldirection (or phase), so that a semiconductor layer coalesced fromseveral nanowires do not exhibit anti-phase domains, i.e. thecoalescence layer 20 is substantially single domain. Preferably thecoalescence layer is grown on nanowires grown in a periodic pattern.

One embodiment of a nanostructured device according to the invention isa nanowire LED, wherein nanowires are part of a LED structure comprisinga pn or pin junction in order to produce light.

In one implementation of the present invention vertical light emittingdiodes (LEDs) based on GaAs nanowires, epitaxially grown Si substrates,have been fabricated. For comparison corresponding LEDs have beenfabricated on GaP substrates. LED functionality has been established onboth kinds of substrates. The structures have been evaluated in terms oftemperature-dependent photoluminescence (PL), electroluminescence (EL),and radiation pattern. Such nanoscale light-sources integrated on the Siplatform may play a major role for future nanophotonics and on-chipoptical communication.

Each LED structure is built around a GaAs NW core, directly grown oneither GaP or Si. Each single GaAs NW acts as the active region in theseindividual nanosized p-i-n light emitting structures.

The LED structures, shown in FIG. 8 b, are p-i-n diode structures. Thesubstrate 3 is an integral part of each device, as it functions as acommon p-layer. This alters a specific sequence of semiconductormaterials in the LED structure depending on what substrate 3 that thenanowires 2 are grown on:

-   -   On GaP the structure the sequence is: p-GaP(substrate        3)/i-GaP(first nanowire segment 13)/i-GaAs(second nanowire        segment 14)/i-InGaP(cladding layer 15)/n-InGaP (cap 16).    -   On Si the structure is: p-Si(substrate 3)/i-GaP(first nanowire        segment 13)/i-GaAs(second nanowire segment 14)/i-InGaP(cladding        layer 15)/n-InGaP (cap 16).

The i-GaP(nanowire) layer in the nanowire base is approximately 60 nmthick in both the devices and serves the dual purposes of a nucleationsegment for improved growth quality and electron barrier. The metalorganic sources used were TMGa and TMIn together with AsH₃, PH₃, andSi₂H₆ as precursor gases. Two growth steps were employed. First, 2 μmlong GaAs/GaP nanowires were grown on p-type GaP (111)B (p=˜10¹⁸ cm⁻³)and Si (111) (p≈10¹⁵ cm⁻³) substrates by particle assisted growth usingrandomly deposited, 60 nm diameter nm sized Au aerosols with a particledensity of 1/μm². The nanowires were capped with 40 nm thick radialInGaP cladding layer, nominally lattice matched to GaAs. After thisstep, samples were unloaded for photoluminescence characterization orsubsequent fabrication of the nanowire LEDs. 80 nm thick SiO₂ wasdeposited onto the samples. The SiO₂ was back etched back to only coverthe substrate surface and up to approximately 1 μm of the nanowire side.The samples were then reloaded into the MOVPE reactor and a radialSi-doped InGaP layer was selectively grown on the upper part of theGaAs/InGaP core structure. The LED structures were fully covered with150-300 nm thick 200×200 μm² quadratic Ni/Ge/Au contacts 17, eachcovering approximately 40000 individual nanowire LED structures.Schematical cross sectional views and scanning electron microscopy (SEM)image of the structure is shown in FIG. 8. The non transparent contact17 on these devices will absorb the majority of the outgoing light,since 10 nm Au absorbs approximately 40% at a wavelength of 850 nm. Thep-contact was fabricated on the backside of the substrate withconductive Ag paste. Other means of contacting are known in the art andeasily adopted to the present method and device.

One important difference between the Si and the GaP device is theheterostructure sequence in the base of the nanowires, on GaP substratebeing p-GaP(bulk)/i-GaP(nanowire)/i-GaAs while on Si substrate beingp-Si(bulk)/i-GaP(nanowire)/i-GaAs(nanowire), where both hole injectionconditions, internal resistance and should be expected to be appreciablydifferent between the two structures.

FIGS. 9 a-c depicts nanowire LED structures after the first MOVPE step.They are GaAs nanowires with a thin InGaP cladding layer and a GaPnucleation segment in the base of the nanowires, and with the Au basedseed particle still attached to the top. Such structures were alsotransferred to neutral substrates for PL characterization. As shown inFIG. 9 the yield with respect to growth direction of the method inaccordance with the present invention is essentially 100 percent on bothGaP and Si substrates, i.e. the fabrication method of these kind ofnanowire structures on Si is improved to the degree that thesubstantially all nanowires are uniformly aligned the (111) directionnormal to the substrates and essentially no nanowires are grown in thethree declined (111) directions that also extends out from thesubstrate. Also, by utilizing the method of the invention this is thefirst realization of growth arrays of III-V vertical nanowires in apredefined ordered pattern on Si substrates, as seen in FIG. 9 c.Control of position and direction of these substrate-grown nanowires arecrucial parameters needed for successful fabrication of optical devices,as well as most other applications. FIG. 9 d schematically illustratesthe LED structure comprising a Si(111)/GaP(111)B substrate 3, a GaPnucleation layer being a first nanowire segment 13, a GaAs nanowire corebeing a second nanowire segment 14, a InGaP cladding layer 15 and a Auseed particle 10.

In one embodiment of a nanostructured device according to the inventionthat is a nanowire LED one of a p or a n region of the pn or pinjunction is at least partly in the substrate 3.

In one embodiment of a nanostructured device according to the inventionthat is a nanowire LED each nanowire 2 at least partly is enclosed in acap layer 16 and the n or p region of the pn or pin junction at leastpartly is in the cap layer 16.

In one embodiment of a nanostructured device according to the inventionthat is a nanowire LED, the nanostructured device comprises common p andn regions formed between nanowires 2.

Photoluminescence (PL) measurements were carried out at room temperatureand at a temperature of 10 K. A laser emitting at 473 nm was used as anexcitation source. The PL was collected by an optical microscope,dispersed through a spectrometer and detected by a CCD camera cooled byliquid nitrogen.

To study the PL from the nanowires without influence of the substrate,the nanowires were broken off and transferred from the substrate wherethey were grown, and then deposited on a patterned Au surface. In thisway the nanowires could also be studied individually. The PL spectraacquired at 10 K from the as-grown nanowires were similar for nanowiresgrown from a Si substrate and the nanowires grown from a Si substrateand the nanowires grown from a GaP substrate. The spectra fromindividual nanowires showed larger differences, with the nanowires grownfrom a GaP substrate being more structured. The average PL intensity forthe nanowires grown from Si was about a factor of 20 lower than for thecorresponding nanowires grown from GaP. This is in fair agreement withthe 10-30 times lower EL seen for the Si-LED as compared to the GaP-LED.At room temperature the spectra are broad and featureless and there isvery little spectral difference between nanowires from the two samples.

Relatively low luminous efficiency in GaAs nanowires have been reportedpreviously and been attributed to stacking faults. Reducing crystallattice strain between the GaAs core and the radially grown InGaP layersis of great importance for the PL intensity, FIG. 10. The individualdiffusion lengths of the In and Ga material and the parasitic growth onGaP and Si surface is very different, requesting an individualfabrication optimization between substrates that could not be fullyperformed in this study.

Both the LED on GaP and on Si demonstrated electro-luminescence whenapplying a forward bias. The spectral peak of the light is in fairagreement with the GaAs bandgap energy.

As seen In FIG. 10 a and b the light power/current dependence is shownfor the Si based and GaP based LEDs. The LED on GaP lights up at halfthe current load (20 mA) of the Si (40 mA) and at 60 mA the power outputis approximately 30 times higher on the GaP substrate. However, at 100mA the power ratio has decreased to 10 times the power ratio of the Sibased LED. The EL spectral peak is shown for 80 mA load for bothdevices. The Si LED peak show a slight red shift and tail with apossible extra peak around 1.35 eV as compared to the GaP substratedevice. The shift in peaks can be explained by the different In and Gadiffusion on GaP and Si leading to different InGaP composition. Bypushing the devices, going to higher currents a peak power can be seenfor approximately 140 mA for the GaP device. This is never seen on theSi device and may be an indication that non-radiative recombination orcompeting leakage mechanisms still dominate the EL at these currentlevels.

FIG. 11 a shows a diagram of power dependence of electroluminescence ofGaAs LEDs grown on GaP and Si and FIG. 11 b shows EL spectra at 80 mAfrom GaP and Si based diodes.

There is a clear difference between the radiation pattern of a devicewhere the seed particle still being attached and one without the Auparticle on the top, as shown in the diagrams of FIGS. 11 c and d,respectively. This is of significance, as these structures have metalcontacts of twice the thickness than the seed particle size. Thisclearly shows that removal of the seed particle may be preferable,especially in a device where vertical extraction of the light is ofimportance.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, on the contrary, it is intended to cover variousmodifications and equivalent arrangements within the appended claims.

1-20. (canceled)
 21. A method of growing at least one III-Vsemiconductor nanowire from a Si surface, the method characterized by astep of providing a group III material pre-flow at a predeterminedelevated temperature to provide a (111)B-like group IIImaterial-terminated Si surface prior to growing of the III-Vsemiconductor nanowire.
 22. The method according to claim 21, whereinthe III-V semiconductor nanowire is grown by particle assisted growthand the method comprises the steps of: providing a group III materialpre-flow at a predetermined elevated temperature giving diffusion ofgroup III material into a growth catalyst particle to provide a(111)B-like group III material-terminated Si surface; introducing groupIII material and group V material precursors at a high temperature togrow a thin III-V nucleation layer with (111)B orientation; and loweringof the temperature to a temperature regime normally used for nanowiregrowth; and growing said at least one III-V semiconductor nanowire fromthe nucleation layer.
 23. The method according to claim 21, wherein themethod comprises the steps of: providing a Ga material pre-flow at apredetermined elevated temperature giving diffusion of the Ga into agrowth catalyst particle to provide a (111)B-like Ga-terminated Sisurface; and introducing Ga material and P material precursors at a hightemperature to grow a thin GaP (111)B nucleation layer-lowering of thetemperature to a temperature regime normally used for nanowire growth;and growing said at least one III-V semiconductor nanowire from thenucleation layer.
 24. The method according to claim 21, wherein themethod comprises the steps of: providing an In material pre-flow at apredetermined elevated temperature giving diffusion of the In into agrowth catalyst particle to provide a (111)B-like In-terminated Sisurface; and introducing Ga material and As material precursors at ahigh temperature to form a thin GaAs (111)B nucleation layer-lowering ofthe temperature to the temperature regime normally used for nanowiregrowth; and growing said at least one III-V semiconductor nanowire fromthe nucleation layer.
 25. The method according to claim 21, wherein aplurality of III-V semiconductor nanowires are grown from the nucleationlayer and the method further comprises the step of growing asemiconductor coalescence layer from the plurality of III-Vsemiconductor nanowires such that the coalescence layer is substantiallysingle domain.
 26. The method according to claim 21, wherein the Sisurface is a Si(111) surface.
 27. A nanostructured device comprising aplurality of III-V semiconductor nanowires grown on a Si(111) surface ofa Si substrate, characterized in that substantially all III-Vsemiconductor nanowires protrude perpendicular to the Si(111) surface.28. The nanostructured device according to claim 27, wherein saidsubstantially all III-V semiconductor nanowires are grown in a (111)Bdirection.
 29. The nanostructured device according to claim 27, whereinthe nanowires are grown on the Si(111) surface in an ordered pattern incompliance with a predetermined device layout.
 30. The nanostructureddevice according to claim 27, wherein said substantially all III-Vsemiconductor nanowires have an angle α to the (111) surface of the Sisubstrate of 90°±5°.
 31. The nanostructured device according to claim30, wherein said substantially all III-V semiconductor nanowires have anangle α to the (111) surface of the Si substrate of 90°±2.5°.
 32. Thenanostructured device according to claim 27, further comprising acoalescence layer grown from the III-V semiconductor nanowires, whereinthe coalescence layer is substantially single domain.
 33. Thenanostructured device according to claim 27, wherein each III-Vsemiconductor nanowire comprises a nucleation segment at a nanowirebase.
 34. The nanostructured device according to claim 32, wherein thenucleation segment is about 60 nm thick.
 35. An electronic oroptoelectronic device comprising the nanostructured device according toclaim
 27. 36. A photonic device comprising the nanostructured deviceaccording to claim
 27. 37. A LED device comprising the nanostructureddevice according to claim 27, wherein the nanowire is part of a LEDstructure comprising a pn or pin junction in order to produce light.